Plate Tectonics & Earth Structure – Science and Technology 10

Plate Tectonics Theory

Modern theory stating that Earth’s lithosphere is broken into moving plates that interact at their boundaries.

Continental Drift Theory

Alfred Wegener’s 1915 idea that continents move across Earth’s surface over geologic time.

Pangaea

Supercontinent that assembled all landmasses about 300 Ma and began breaking apart ~200 Ma.

Rodinia

Older supercontinent that existed before Pangaea and split into Laurasia and Gondwanaland.

Laurasia

Northern supercontinent formed from Rodinia’s breakup; included North America, Europe, and Asia.

Gondwanaland (Gondwana)

Southern supercontinent containing South America, Africa, India, Australia, and Antarctica after Rodinia split.

Lithosphere

Rigid outer shell of Earth comprising crust and uppermost mantle; broken into tectonic plates.

Asthenosphere

Hot, semi-plastic mantle layer beneath the lithosphere that allows plates to move.

Crust

Earth’s outermost solid layer; includes continental and oceanic varieties.

Continental Crust

Thick (10–70 km), buoyant, granitic crust that is generally old.

Oceanic Crust

Thin (~7 km), dense, basaltic crust that is relatively young.

Mantle

Silicate rock layer between crust and core, extending to about 2,900 km depth.

Core

Innermost layer of Earth, composed mainly of iron and nickel, with liquid outer and solid inner parts.

Isostasy

Concept by Clarence Dutton that crustal blocks float in gravitational balance so equal masses underlie equal areas.

Raisin Theory

Obsolete idea that Earth cooled, contracted, and wrinkled like a raisin to form mountains.

Tectonic Plate

Large, rigid slab of lithosphere that moves atop the asthenosphere.

Mid-Ocean Ridge

Continuous undersea mountain chain where new oceanic crust forms at divergent boundaries.

Sea-Floor Spreading

Harry Hess’s hypothesis that new seafloor forms at mid-ocean ridges, pushing continents apart.

Paleomagnetism

Symmetrical magnetic patterns recorded in oceanic crust that confirm sea-floor spreading.

Alfred Wegener

German scientist who proposed Continental